Process of making artificial silk



y 7, 1935- H. G. STONE 2,000,048

PROCESS OF MAKING ARTIFICIAL SILK Filed Sept. 21, 1932 Airrmzi Heat Outlet W 0 EV Airm' Heaibzlei HerberZGSiOne, I I gwumto'v:

' ucts.

Patented May 7, 1935 PATENT OFFICE PROCESS OF MAKING ARTIFICIAL SILK Herbert G. Stone, Kingsport, TennJ, assignor to Eastman Kodak Company, Rochester, N. Y.,' a corporation of New York Application September 21, 1932, Serial No. 634,185

6 Claims.. (01. 1854) This invention relates to the manufacture of artificial silk, and more particularly to an improved process for producing filaments by the dry-spinning method in which a solution of a cellulose derivative is extruded into an evaporative atmosphere.

Many different investigators have studied the conditions prevailing in the manufacture of artificial silk and much work has been done with a view to determining the conditions which should be maintained within the spinning cell in order to produce the most satisfactory prod- It has been found that control of temperatures is an important item and in'my copending application, Serial No. 560,191, filed August 29, 1931, I have described and claimed a process wherein certain definite temperature relations are specified. In continuing this work further, I have discovered that there is a very definite and critical relation between the temperature of the solution extruded into the spinning cell, the temperatures of the various portions of the evaporative atmosphere of the cell, and the type of product obtained.

I have found that when these temperature relations are controlled in the manner herein after described a filament having a rounded cross section, great tensile strength and excellent appearance is produced.

The present invention has as its principal object to provide a process for obtaining artificial filaments having an approximately round cross section in contrast to filaments produced in known silk spinning operations in which the filaments have an elliptical cross section.

Another object is to provide a process in which the physical characteristics of the filaments such as tensile strength and appearance may be controlled by a control of the temperature of the spinning solution and the temperatures prevailing in the various zones of the spinning cabinet or cell. Other objects will hereinafter appear.

These objects are accomplished by the following invention which, stated in simplest terms, may be said to comprise the extrusion of a solution of a cellulose derivative, such as cellulose acetate dissolved in an appropriate solvent,-

through a spinning die into an evaporative atmosphere in a closed cell in which a current of gaseous evaporative medium is maintained. I have found that, in order to produce the desired type of filament, the temperature of the solution at the die or spinneret just before extrusion must be maintained at a temperature which is substantially higher than that of the evaporative atmosphere into which it is first extruded, but lower than the temperature of the current of gaseous evaporative medium passing through the main portion of the cell. In other words, the temperature of the solution initially spun is higher than'that of the atmosphere in the upper part of the cell, but lower than that of the atmospherein the remainder thereof.

Upon the first point namely maintenance of solution temperature above the temperature of the immediately adjacent spinning zone, as well as passage of the filament then thruv a current of air at a higher temperature, this application continues and relates to the subject matter of my copending application Ser. No. 560,191 filed August 29, 1931, altho the instant invention is a distinct advance over the subject matter of the prior application. I

In the following examples and description I have set forth. several, of the preferred embodi- 20 ments of my invention, but they are included merely for purposes of illustration of the general principles of my invention and not as a limitation thereof. g

The invention may be best described by reference to the accompanying drawing in which like reference characters refer to like parts and in which:

Fig. 1 is a side elevation of a unit of a spinning machine which may be employedin producing artificial silk according to the invention.

Fig. 2 is a section at right angles to the view shown in Fig. 1, taken along the line 2-2 of that figure. i

The spinning solution may consist of a solution of any one of a number of organic derivatives of cellulose dissolved in any one or a mixture of appropriate solvents. The solution may consist, for example, of a to solution of cellulose acetate in acetone. If desired, a' solution of cellulose acetate-propionate in acetone, ethylene chloride, or other volatile solvent suitable for the production of artificial silk, such as those described and claimed in the application of H. .T. Clarke and C. J. Malm Serial No. 560,- 208 may be utilized for the production of filaments according to my process. It will be apparent that the composition of these spinning solutions may vary rather widely as to the cel- 50 lulose derivative itself, its concentration in the solution and the solvent or solvent combination in which it is dissolved. I have found, other things being equal, that the higher the percentage of solids in the solution, the fatter and a heating jacket 5 supplied with a heating fiuid,

such as water or other suitable liquid or vapor, which enters the bottom of the jacket through the inlet 1 and passes out at the top through the outlet 8 for heating the spinning solution to the final temperature desired. The candle filter may of course be heated by a zone or space around the filter in the manner described in my copending application referred to above. passing through the candle filter 5 the solution is extruded through fine orifices in the spinning die or spinneret 9 in the form of fine filaments or" rounded cross section. As these filaments proceed down the cabinet the solvent is evaporated therefrom in a manner to be more fully described, the finished filaments being brought together at a common point at the guide roll I over which they pass, thence through a minute opening H in the wall of the cabinet to a drawroll 12. From the draw-roll the filaments are conducted over guide 13 and through guide I4 to spinning pot or bobbin l5 where they are spun into the desired thread. The bobbin may be rotated by means of a motor H3 or other suitable source of power, which may also be employed for reciprocating the guide I4 in any desired manner. The well known'cap-spinning device may likewise be used to effect the wind up of the thread.

The walls of the spinning cabinet I! may be provided with any suitable heat-insulating material. It may be said that, other things being equal, the less susceptible a material is to the conduction of heat, the more suitable it is to be employed partly or wholly in the construction of the walls of the spinning cell. The cell I1 is provided with an inlet l8 through which a supply of suitable gaseous evaporative medium is passed into the interior thereof. The evaporative medium after passing up the cell finally emerges through the outlet l9 which is located at a point approximately one-third of the way down from the top of the spinning cell. The gaseous medium is preferably heated air, but it is within the scope of my invention to employ nonreactive gaseous evaporative media other than air if desired. It will be apparent to those skilled in-the art that such gaseous media should be substantially inert and have no deleterious action upon the filaments being produced.

According to the principles of my invention it is necessary that certain definite temperature relations be maintained between the various, portions of the apparatus. I have discovered that in order to produce my improved type of'filament the temperature of the spinning solution should be maintained considerably higher than that of the immediate evaporative atmosphere into which it is extruded. As will be apparent After 7 have a temperature preferably of about 72 C. t is preferable to pass the heating fluid in at the bottom of the heating jacket in order that the highest temperature may be maintained at that point in the apparatus in closest proximity to the spinneret, the fluid finally passing out through the outlet 8.

The temperature differential between the so1ution and the atmosphere into which it is extruded will be apparent by reference to Fig. l in which I have indicated certain suitable temperatures which are given merely for purposes of illustration but without intending to limit my invention in any way. It will be seen that a considerable drop in temperature of the solution occurs as it emerges from the spinneret and this is one of the conditions of operation which I have found necessary in order to produce the improved filaments herein described. Any suitable means of providing this difference in temperature may be employed but I have found it may be most conveniently accomplished by 10- cating the spinning die in the top portion of the cabinet, with the outlet for the heated evaporative atmosphere located approximately one third of the way down the cabinet. This arrangement provides a dead zone or zone in which very little circulation of the spinning atmosphere takes place, thereby producing a relatively cool space, partially saturated with solvent vapors,

in which the early stages of evaporation of solvents from the filaments may take place. I have found that this relatively slow initial evaporation results in a better control of the stretch characteristics of the filaments. If desired, this required cooling of the evaporative atmosphere into which the filaments are first extruded may be accomplished or assisted'by placing cooling coils in the zone just below the spinning die, or even by surrounding that portion of the cabinet by a cooling jacket, altho I have found that air cooling of this zone is generally sufficient.

I have also discovered that a definite relation exists, not only between the temperature of the spinning solution and the atmosphere into which it is extruded, but also between the temperature of the solution and the temperature of the current of evaporative atmosphere maintained in the cell. I have found, for example, that the spinning solution temperature should be lower than the temperature of any portion of the gaseous current. The inlet temperature may, for example, be maintained at about 110 0., while its outlet temperature is about 74 C. The gaseous medium, preferably air, may be heated and kept in motion by any suitable means (not shown). v

From the above description it will be seen that the spinning solution passes first through a zone of relatively high temperature in the candle filter, emerges into an evaporative atmosphere of much lower temperature and finally meets and travels through an evaporative atmosphere of increasing temperature until it eventually leaves the spinning cell. It should be noted that the temperature conditions just described may be satisfactorily maintained by employing a structure such as that shown in Fig. 1, in which a strong heated current of air or other gaseous medium is maintained through the lower twothirds of the spinning cell while what may be referred to as a dead zone or zone in which no substantial movement of evaporative atmosphere occurs exists at the upper portion of the cell. It is in this latter zone that the temperature of the spinning solution ismarkedly lowered as it emerges from the spinneret. The drop in temperature from the inlet to the outlet may be regulated by regulating the speed of the air thru the cabinet (more air, of course, supplying more heat and permitting less drop in temperature) or by insulating the cabinet or'by supplemental heating of the cabinet, altho air regulation is normally suilicient.

The following examples are typical of spinning operations carried out according to the principles of my invention.

Example I A 25% solution of hydrolyzed cellulose acetate is made up employing acetone as the solvent. The solution is well filtered and then pumped through the candle filter located as shown in the drawing at the top of the spinning cabinet. The candle filter and spinneret is maintained at a temperature of 72 C. by passage of heating fluid through the heating jacket 6. The spinning solution is forced out through the spinneret 9 into the spinning cabinet through which a current of heated air is passed at a rate of about 20 cu. ft. per minute for the production of thread of approximately 150 denier. The current of air enters the lower part of the cabinet through the inlet i8 at a temperature of about 110 C., progresses up the cabinet and finally leaves it through the outlet !9 at a temperature of about 74 0. As the filaments are formed, they progress down the cabinet, first through a zone having a temperature ranging from 56-63 C., and finally through a zone having a temperature of about 74-110" C. These filaments meet at a common point on the guide l0 and are drawn from the cabinet by means of draw roll l2 which is rotated at a circumferential speed of about 1.8 times the rate of extrusion of the solution through the spinneret thus stretching and elongating the filament during its coagulation. A cellulose acetate silk of 150 denier, of uniform round cross section, and having excellent tensile strength and appearance results and is wound on bobbin l5.

Example II A 20-25% spinning solution is made up by dissolving hydrolyzed cellulose acetate in acetone as the solvent. This solution is spun in exactly the same manner as in the previous example, except that the temperature of the spinneret is maintained at about 67 C., the temperature in the portion of the spinning cell immediately below the spinneret is about 55-65 C., the inlet temperature of the gaseous evaporative medium passing through the lower two thirds of the cell is maintained at about 120 C. and the outlet at about 89 C. The volume of air passing through the cell is 23 cu. ft. per minute.

Example III The cellulose acetate propionate having a propionyl content of about 20% is dissolved in acetone to form a solution of approximately 26% strength. This solution was used under the same conditions as described in Example I, except that the temperature of the solution as it emerges from the spinneret is maintained at 70 C., the temperature of the zone just below the spinneret at about 55-60 C., the temperature of the air entering the cabinet at about 100 C. and that of the air leaving the cabinet at about 74 C.

It will be obvious that many changes may be made in the details of the process as herein described as well as in apparatus for carrying out the process. For example, the height of the spinning cabinet may be varied according to the judgment of the individual operator. A cabinet of greater height will take up more space than a shorter cabinet, but will permit a greater lineal speed in filamenting than a short cabinet; A-

spinning cabinet having a length of 12-18 ft., which is commonly employed in spinning artificial silk, will be preferred for most purposes and will be found quite satisfactory and of large capacity. Spinning cells 12 ft. high allow a spinning speed of about 180 metres per minute with a 25% acetone solution of cellulose acetate. When the spinning cell is lengthened obviously the spinning speed may be increased as the filament may travel faster in a longer cabinetand still be under treatment for the same amount of time as if the filament were traveling more slowly in a shorter cabinet. For example, if the height of the spinning cabinet is 24 ft., aspinning speed of 240-300 metres per minute may be employed for the same type of spinning solution as just indicated.

It is generally preferred that the freshly formed filaments be under some tension. This so-called stretch spinning may be accomplished by rotating the draw-roll l2'at a circumferen-' tial speed which is greater than extrusion speed in the spinning die, for instance, from 1.5 to 2 times greater. For example, if the extrusion speed of the solution passing through the spin neret is 180 metres per minute then a draw-roll of 8 cm. diameter may be rotated at aratej of about 1300 R. P. M. to accomplish a suitable stretch of the filaments in the spinning operation.

The temperatures indicated in the above description are intended merely to be illustrative, as it will be apparent that these temperatures will vary in accordance with the particular type of spinning solution dealt with, the spinning speed, the volatility of solvents employed and various other factors known to those skilled in the art. In dealing with spinning temperatures according to the principles of my invention it is merely necessary that the relation between the spinning solution temperature, the temperature of the evaporative atmosphere into which it is extruded and the temperature of the current of gaseous evaporative medium be maintained substantinally as specified. While I have found that a differential of 10-20 C. between the temperature of the spinning solution and that of the atmosphere into which it is extruded is satisfactory, I may employ a smaller or a greater differential if desired. Likewise, the difference in temperature of the gaseous current is satisfactorily maintained at 1-25 C., but may be greater or less if desired. It may be said at this point that the outlet temperature is dependent upon the inlet temperature and it is, of course, evident that the inlet temperature will always be higher than the outlet temperature and will therefore be considerably higher than the temperature of the spinning solution as it enters the spinning cell.

What I claim is: I

1. The process of making artificial silk by the dry spinning method vwhich comprises heating a solution of an organic ester of cellulose in a volatile solvent to a temperature above room temperatures, but below the decomposition temperature of the ester, extruding the heated solution in the form of a filament into a zone of evaporative medium of lower temperature than the solution and then into a current of evaporative medium of progressively higher temperature with progress of the filament therethrough, all points of which evaporative medium are maintained above the spinning solution temperature, but below the decomposition temperature of the ester, none of the foregoing temperatures being substantially in excess of 120 C.

2. The process of making artificial silk by the dry spinning method which comprises heating a solution of an organic ester of cellulose in a volatile solvent to a temperature above room temperatures, but below the decomposition temperature of the ester, passing the heated solution through a spinneret, whereby filaments are formed, conducting the filaments through a zone of substantially immobile evaporative atmosphere of lower temperature than the spinning solution, and then through a current of evaporative medium maintained at a temperature higher than that of the spinning solution, but below the decomposition temperature of the ester, none of the foregoing temperatures being substantially in excess of 120 C.

3.- The process of making artificial silk by the dry spinning method which comprises heating a solution of an organic ester of cellulose in a dry spinning method which comprises passing a heated solution of an organic ester of cellulose in a volatile solvent through a spinneret, whereby filaments are formed, conducting the filaments through a zone of substantially immobile evaporative medium of lower temperature than the solution, and then through a current of evaporative medium heated progressively higher in the direction of travel of the filament therethrough to temperatures above room temperature, but below the decomposition temperature of the ester, said solution being heated immediately prior to filamenting to a temperature higher than that of the immobile zone, but lower than that of any portion of the current of evaporative' medium, none of the foregoing temperatures being substantially in excess of 120 C.

5. The process of making artificial silk by the dry spinning method which comprises passing a heated solution of an organic ester of cellulose in a volatile solvent through a spinneret, whereby filaments are formed, conducting the filaments through a zone of substantially immobile evaporative medium heated to a temperature 1 above room temperature but below 74 C., and then through a current of evaporative medium heated progressively in the direction of travel of the filaments therethrough to temperatures Within the range of 74-120 C., said solution being heated immediately prior to filamenting to a temperature higher than that of the zone into which it is first extruded, but below 74 C.

6. The process of making artificial silk by the dry spinning method which comprises passing a heated solution of cellulose acetate in a volatile solvent through a spinneret, whereby filaments are formed, conducting the filaments through a zone of substantially immobile evaporative medium heated to a progressively increasing tem- 'mediately prior to filamenting to a temperature above 65 0., but below 74 C.

HERBERT G. STONE. 

